The present invention relates to novel asymmetric silicon-bridged metallocenes useful as catalysts for the polymerization of xcex1-olefins. It relates more specifically to novel silicon-bridged metallocenes containing an indenyl and a partially or fully hydrogenated fluorenyl moiety and to a process for their preparation. Finally it relates to a process for polymerization of xcex1-olefins by using said asymmetric silicon-bridged metallocenes.
Some asymmetric silicon-bridged metallocenes derived from group 4 metals and containing fluorenyl and indenyl moieties have already been proposed for the polymerization of xcex1-olefins such as ethylene and propylene. For example, the use of silicon-bridged (9-fluorenyl)-(1-substituted indenyl) zirconium dichlorides in combination with aluminoxanes for the polymerization of xcex1-olefins is disclosed in EP-A-0 754 698 and Macromolecules, 2000, 33 (5), 1546. However, the productivity and stability of such metallocenes remain insufficient.
Symmetric silicon-bridged bis(octahydrofluorenyl)zirconocenes and their use as catalysts for the polymerization of ethylene have been reported by Nxc3xa4sman et al. (J. Organomet. Chem., 1997, 545, 219) and are decribed in WO 95/27717. The latter also discloses the use of symmetric silicon-bridged bis(tetrahydrofluorenyl)zirconocenes. However, these zirconocenes are not suitable for the production of isotactic polypropylene.
Accordingly, there is still a need for silicon-bridged metallocene catalysts containing indenyl and fluorenyl moieties yielding very stereoregular polypropylene with high catalytic activity.
It is an object of the present invention to solve the above-mentioned problems by providing novel stable metallocenes useful as catalysts for xcex1-olefin polymerization which are, in particular, able to produce, with a particularly high activity, polyethylene and highly stereoregular polypropylene and a process for preparing such metallocenes. It is another object of the present invention to provide a process for polymerization of the xcex1-olefins by means of said metallocenes.
The invention is thus related to novel asymmetric silicon-bridged metallocenes of formula (I):
(SiRxe2x80x2Rxe2x80x3)(Cp)(Cpxe2x80x2)MXXxe2x80x2xe2x80x83xe2x80x83(I) 
wherein
Cp is a partially or fully hydrogenated fluorenyl moiety selected from those of formula (II) and (III) 
Cpxe2x80x2 is an indenyl group selected from those of formula (IV) 
M represents a transition metal selected from Ti, Zr and Hf,
X and Xxe2x80x2 represent, same or different from each other, a halogen atom,
R1, R2 and R3 are, same or different from each other, an alkyl group containing 1 or 2 carbon atoms, an aryl group containing from 6 to 10 carbon atoms or a hydrogen atom,
(SiRxe2x80x2Rxe2x80x3) is a divalent group which bridges the two groups Cp and Cpxe2x80x2 repectively on position 9 and 1,
Rxe2x80x2 and Rxe2x80x3 are, same or different from each other, an alkyl or aryl group containing from 1 to 10 carbon atoms.
The invention also relates to a process for the preparation of these metallocenes.
Metallocenes of formula (I) wherein Cp is a tetrahydrofluorenyl group selected from those of formula (II) are preferably prepared by a route comprising the following steps:
a) production of 9-(1,2,3,4-tetrahydrofluorenyl)-1-(indenyl (or substituted indenyl))-dialkyl(or diaryl)silane from the (indenyl (or substituted indenyl))-dialkyl(or diaryl)-chlorosilane and 1,2,3,4-tetrahydrofluorenyllithium,
b) production of the dilithium salt of 9-(1,2,3,4-tetrahydrofluorenyl) (1-indenyl (or substituted indenyl))-dialkyl(or diaryl)silane precursor and
c) production of the metallocene by reacting the said dilithium salt with a halide of one of the transition metals mentioned hereabove.
Metallocenes of formula (I) wherein Cp is an octahydrofluorenyl group of formula (III) are preferably prepared by a route comprising the following steps:
axe2x80x2) production of 9-(1,2,3,4,5,6,7,8-octahydrofluorenyl)-1-(indenyl (or substituted indenyl))-dialkyl(or diaryl)silane from (indenyl (or substituted indenyl))lithium and 9-(1,2,3,4,5,6,7,8-octahydrofluorenyl) dichloro-dialkyl (or diaryl)silane,
bxe2x80x2) production of the dilithium salt of 9-(1,2,3,4,5,6,7,8-octahydrofluorenyl)-1-(indenyl (or substituted indenyl))-dialkyl(or diaryl)silane precursor and
cxe2x80x2) production of the metallocene by reacting the said dilithium salt with a halide of one of the transition metals mentioned hereabove.
Finally the present invention relates to a process for polymerization of xcex1-olefins by means of said metallocenes.
According to a first aspect, the present invention relates to novel stable metallocenes of the above general formula (I).
Preferably the transition metal is selected from hafnium and zirconium. Most preferably the transition metal is zirconium.
The halogen atoms X and Xxe2x80x2 are preferably chlorine or bromine atoms and most preferably they are both chlorine atoms.
The group R1 represents preferably a methyl group.
The groups R2 and R3 represent preferably a methyl group, an aryl group containing from 6 to 10 carbon atoms or a hydrogen atom, with at least one of R2 or R3 being different from hydrogen. Most preferably R2 is a hydrogen atom and R3 is a phenyl group.
The groups Rxe2x80x2 and Rxe2x80x3 are preferably alkyl groups and more particularly alkyl groups containing from 1 to 3 carbon atoms. Most preferably Rxe2x80x2 and Rxe2x80x3 are a methyl group.
Among the most preferred metallocenes according to the present invention belongs the dimethylsilylene-[xcex75-1-(2-methyl-4-phenyl)indenyl]-[xcex75-9-(1,2,3,4,5,6,7,8-octahydrofluorenyl)] zirconium dichloride. Another example of most preferred metallocenes according to the present invention is the dimethylsilylene-[xcex75-1-(2-methyl-4-phenyl)indenyl]-[xcex75-9-(1,2,3,4-tetrahydrofluorenyl)] zirconium dichloride.
When used in combination with a cocatalyst, such as for example aluminoxane, said novel stable metallocenes are able to produce with a high activity polyethylene and highly stereoregular polypropylene.
According to a second aspect, the present invention relates to a process for producing the novel metallocenes of general formula (I) as described hereabove.
Preferably, step (a) is carried out by reacting the 1,2,3,4-tetrahydrofluorenyllithium with the chlorosilane in equimolar quantity.
Preferably, step (b) is carried out with at least two molar equivalents of butyllithium per mole of the 9-(1,2,3,4-tetrahydrofluorenyl)-1-(indenyl (or substituted indenyl))-dialkyl(or diaryl)-silane precursor, followed by reacting the obtained dilithium salt with one equivalent of transition metal halide.
Preferably, the step (a) is carried out in an inert solvent such as diethylether or a mixture of these, most often at about 0xc2x0 C. At the end of the reaction, the suspension is usually hydrolyzed and the organic phase is isolated. After removal of the solvent, the 9-(1,2,3,4-tetrahydrofluorenyl)-1-(indenyl (or substituted indenyl))-dialkyl(or diaryl)-silane precursor is isolated.
Preferably, step (b) is carried out in an inert solvent, such as diethylether, hexane, pentane or tetrahydrofuran (THF) often at 0xc2x0 C. The resulting lithium salt is advantageously separated from the solvent and washed prior to being reacted, in step (c), with about one equivalent of a transition metal halide selected from halides of Ti, Zr and Hf.
Step (c) is preferably carried out in an inert solvent, such as an ether, often at 0xc2x0 C. After removal of the solvent, the solid metallocene of formula (I) wherein Cp is a group selected from those of formula (II) is isolated as a mixture of isomers.
Preferably, steps (axe2x80x2), (bxe2x80x2) and (cxe2x80x2) are carried out in the same way as respectively the preferred steps (a), (b) and (c) for metallocenes of formula (I) wherein Cp is a group selected from those of formula (II). The 9-(1,2,3,4,5,6,7,8-octahydrofluorenyl)chloro-dialkyl(or diaryl)silane is generally synthesized as described in Organometallics, 1997, 16, 2503.
The novel metallocenes according to the present invention are useful as catalysts for the polymerization of xcex1-olefins. The reaction is carried out by contacting said xcex1-olefins with the said metallocene under polymerization conditions. It can be carried out in solution or in suspension in a hydrocarbon diluent or in suspension in one of the monomers maintained in the liquid form or in the gas phase. The polymerization conditions are well known by persons skilled in the art.
The metallocenes according to the invention can be used in combination with each other. They can also be used in combination with aluminoxanes. Methylaluminoxane (MAO) is preferred. They can also be used in combination with an ionizing agent. This ionizing agent can be chosen from the compounds comprising a first part which has the properties of a Lewis acid and which is capable of ionizing the metallocene and a second part that is inert towards the ionized metallocene. Examples of ionizing agents are triphenylcarbenium tetrakis(pentafluorophenyl) borate, N,Nxe2x80x2-dimethylanilinium tetrakis(pentafluorophenyl) borate, tri(n-butyl)ammonium tetrakis(pentafluorophenyl)borate, tri(pentafluorophenyl)boron, triphenylboron, trimethylboron, tri(trimethylsilyl)borate and organoboroxines.
Organometallic compounds are generally used as cocatalysts and/or poison scavengers. They can be selected from organometallic compounds of lithium, magnesium, zinc, aluminium or tin. The best results are obtained with organoaluminium compounds and in particular with trialkylaluminium compounds.
The xcex1-olefins can be chosen from those containing up to 20, preferably up to 12 carbon atoms per molecule. The xcex1-olefin is preferably ethylene or propylene. The metallocenes according to the present invention may be used for the homopolymerization of one of these xcex1-olefins or for the copolymerization-random or block copolymerization-of one of these xcex1-olefins with one or more comonomers. The preferred comonomers of ethylene are butene, hexene and their mixtures. The preferred comonomers of propylene are ethylene, butene and their mixtures.
The novel metallocenes according to the invention are stable molecules and are especially well adapted to polymerize with a particularly high activity ethylene and propylene, and are able to produce highly stereoregular polypropylene.
In addition to the foregoing description of the invention, the following examples are provided to illustrate the present invention.
In these examples reactions are carried out under an argon atmosphere using standard Schlenk techniques. Diethyl ether, THF, hexane and pentane were distilled from Na/K alloy under argon. Dichloromethane was distilled from CaH2 under argon. MAO was purchased as a solution in toluene from Akzo Nobel and used as received. All other reagents were purchased from Aldrich and used without further purification.
Melting points (Tm) of the polymers were determined by DSC with a Perkin-Elmer DSC-System. 13C NMR spectra for pentad (mmmm in mol %) analysis were determined on an AMX500 spectrometer at 90xc2x0 C. in C6H3Cl3 with C6D6. Triad (mm in mol %) analysis was performed on 13C NMR spectra recorded on an AC-200 spectrometer at 120xc2x0 C. in C6H3Cl3.1H NMR spectra were recorded on a AC-200 spectrometer at room temperature in CDCl3. Molecular masses were determined by High Resolution Mass Spectrometry (HRMS). The molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the polymers were determined by gel permeation chromatography (GPC-150C apparatus manufactured by Waters Co Ltd) recorded at 135xc2x0 C. using a trichlorobenzene solution having a polymer concentration of 0.5 g/l and a polystyrene gel column, e.g. Waters Styragel HMW 6E available from Waters Co. Ltd.
1. Preparation of Metallocenes